Dawn Nguyen is escorted into the Federal Building in Rochester and charged in connection with the guns used in the Christmas Eve 2012 ambush slaying of two volunteer firefighters responding to a house fire in Webster, in upstate New York.

The families of four New York state firefighters are suing St. Paul-based Gander Mountain, alleging that the retailer could have prevented a “straw buyer” from purchasing a rifle used in a deadly Christmas Eve 2012 ambush.

The suit, which has the support of prominent gun control advocates, said the rifle used in the bloody predawn incident should never have been sold to a woman who came to a Rochester, N.Y., store in June 2010 with the eventual shooter at her side.

The families said in a joint statement that they originally believed the four had been shot in “yet another random act of violence. … But as time went by, new and very troubling facts emerged. These facts suggest that the loss we have endured could have been avoided. If only the store had acted responsibly.”

A spokesman for Gander Mountain, the nation’s largest outdoors outfitter, said the company had been forthcoming in the investigation and is committed to safety.

Shelley Leeson, who heads the Twin Cities Gun Owners & Carry Forum, said trying to hold Gander responsible for the incident was “bogus.” She accused the advocates behind the suit of “playing the emotions of the victims’ families to further their gun control agenda to punish manufacturers and retailers.”

She added that it appears Gander Mountain followed the legally required procedures for the sale and “cannot be held responsible for second-guessing the intentions or future actions of every purchaser.”

Along with payment of punitive and compensatory damages to the firefighters’ families and the two survivors, the suit seeks to have Gander Mountain reform its practices and employee training procedures to block “straw purchasers.” The suit was filed Tuesday in state court in Rochester.

In the 2012 incident, William Spengler, 61, torched his home and then opened fire on emergency responders, fatally shooting two West Webster, N.Y., firefighters, Tomasz Kaczowka and Michael Chiapperini, and wounding two others, Ted Scardino and Joseph Hofstetter.

Shortly before setting the fire, Spengler used a handgun to kill his sister in the childhood home they shared. He shot and killed himself later that morning.

The families filing the suit voiced support for the constitutional rights of gun owners and said that “some of us, in fact, own guns.

“But,” they said, “we also believe that companies who make it their business to sell guns must do so in a responsible and lawful manner. And when sellers fall short in their responsibility, they should be held accountable.”

The suit spells out that gun buyer Dawn Nguyen entered Gander Mountain with Spengler, who was prohibited from owning firearms after a conviction for killing his 92-year-old grandmother with a hammer. Nguyen, Spengler’s neighbor, filled out the required state and federal forms identifying herself as the purchaser and paid $1,425 in cash for a semi-automatic rifle and a shotgun.

Gander Mountain’s staff should have known that the purchase was being made for someone who was barred from possessing firearms, the suit continued, pointing out that the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives has warned that indicators of a straw purchase include multiple firearms being bought in one transaction, more than one person entering the store together and purchases made with cash.

Nguyen, now 24, was convicted in April of falsifying a firearms form when she bought the guns. She was sentenced Monday to at least 16 months in prison. She and Spengler’s estate are named as co-defendants in the suit.

The families’ legal team in this action includes the Brady Center to Prevent Gun Violence, which was founded in 1974 as the National Council to Control Handguns and has for decades been lobbying for stricter gun laws. Its name changed upon former White House press secretary Jim Brady and his wife, Sarah, becoming members in the mid-1980s

“Gun dealers have a responsibility to ensure they are selling guns to people legally entitled to purchase them,” said Jonathan Lowy, director of the Brady Center’s Legal Action Project, which has been steadily filing suits such as these against gun sellers across the country. “Just like a bar has a responsibility not to sell alcohol to minors, Gander Mountain has a responsibility not to sell firearms to convicted criminals.”

In one of those “straw buyer” suits, the parents of slain off-duty Chicago police officer and a Mississippi pawnshop agreed that the shop will enact policies that exceed those dictated by state and federal laws addressing handgun sales. The policies include, among other provisions, the video recording of all handgun sales and three-year storage of the recordings.